From U.S. Pat. No. 3,079,204, bearing structures are already known which are provided with a dry lubricant film. The film, as solid lubricant substance, contains molybdenum disulfide, with or without additional graphite, and contains, as binding agent, a dried water-soluble metal silicate. The lubricant film is preferably composed of at least 50 to not more than 87% molybdenum disulfide, b 0-7.7% graphite, and 50-13% dried, water-soluble metal silicate. The lubricant film is applied from an aqueous suspension of the individual solid components; this suspension contains enough water to dissolve the water-soluble metal silicate, so that, with the solid lubricant substance, it can form a workable, uniform mixture. Such aqueous compositions indeed produce usable lubricant films, but they are unstable and lead to aggregates, and in this way the viscosity of such dispersions is increased, and, moreover, in a fashion which is uncontrollable. The use of such aqueous compositions is accordingly limited to those applications in which a dry lubricant film is immediately formed, and thus these compositions have no significance as directly usable liquid aqueous lubricants.
In U.S. Pat. No. 4,088,585, a composition is described which is suitable for the formation of dry lubricant films on metal workpieces; the composition consists of powdered molybdenum disulfide, soluble silicate from silicon dioxide, sodium oxide and/or potassium oxide, hydroxyethylcellulose, and water as the remainder. The quantity of powdered molybdenum disulfide in general is about 5-30%, preferably about 10-30%. The soluble silicate is in general present in a quantity of 0.6-12%, and here the weight ratio of silicon dioxide to sodium and/or potassium oxide is more than about 1.5 and less than about 4. The content of hydroxyethylcellulose is in general between 0.2 and 3%. The lubricant composition can, along with the indicated essential components, also contain small quantities of a biocide and an antifoam additive.
The aforementioned aqueous lubricants indeed supply an adequate lubrication to workpieces, but they have the disadvantage that, like all lubricants containing silicate, they do not adhere adequately to the part to be lubricated, so that the lubricant effect which can be achieved with them is only of limited duration.
From German Patent Application No. 1,815,829, stable aqueous lubricants are known which are suitable for the formation of dry liquid films, and these lubricants consist of
1. an aqueous solution of an alkali metal silicate and an alkali metal lignosulfonate, as dispersing phase, PA1 2. a finely divided dry-film lubricant as disperse phase and, on occasion PA1 3. a wetting agent. PA1 (a) about 60-80 wt %, especially 65-75 wt % water; PA1 (b) about 15-30 wt %, particularly about 18-25 wt %, of a solid lubricant combination of molybdenum disulfide and graphite, in a weight ratio of about 1.5-2.5:1, PA1 (c) about 5-10 wt %, particularly about 6-8 wt %, acrylic resin as binding agent, and here the components (a), (b) and (c) combine to 100 wt %; PA1 (d) about 0.1-2 wt %, particularly about 0.4-0.8 wt %, of a dispersing and/or wetting agent, relative to the total quantity of the components (a), (b) and (c); and PA1 (e) on occasion, about 0.1-1 wt %, especially about 0.3-0.7 wt %, of the additional auxiliary substances, relative to the total quantity of the components (a), (b) and (c). PA1 (e 1) a thickening agent, PA1 (e 2) a rust inhibitor, PA1 (e 3) a preservative and/or PA1 (e 4) an antifoaming additive.
The dry-film lubricant is preferably molybdenum disulfide and/or graphite with an average particle size of less than about 1.mu.. The aqueous dispersing agent phase in general contains about 30-40 parts by weight water, about 30-40 parts by weight alkali metal silicate (preferably sodium or potassium silicate) and 0.25-5 parts by weight alkali metal lignosulfonate, such as potassium or sodium lignosulfonate, in general, about 25-35 parts by weight dry solid lubricant are dispersed in this phase. On occasion, wetting agents can also be present. A preferred composition contains about 35 parts by weight water, about 35 parts by weight alkali metal silicate, about 30 parts by weight dry-film lubricant, about 0.5 parts alkali metal lignosulfonate, and about 0.1 parts wetting agent.
In comparison to the aqueous lubricants already described, the lubricant above indeed has the advantage of adequate stability, while at the same time, like all lubricants containing silicates, there is a significant disadvantage: the lubricant film obtained in the manner described does not adhere adequately to the given carrier. The attainable lubricant effect is thus only of limited duration.
The invention now has the task of creating a new aqueous lubricant which, with a lubricant effect which is comparable to, or even better than, the known aqueous lubricants, results in a significantly longer duration for the lubricant effect. The aqueous lubricant to be created should be compatible with the environment and should not have an unpleasant odor, i.e., it should not contain organic solvents or substances with annoying odors, it should be easy to apply in a manner suitable for industrial mass production, and it should dry rapidly.